The hamster cheek pouch preparation as a model for studies of macromolecular permeability of the microvasculature

Protective effects of Ruscus extract in combination with ascorbic acid and hesperidine methylchalcone on increased leukocyte-endothelial interaction and macromolecular permeability induced by ischemia reperfusion injury

BACKGROUND

Despite the well-recognized effectiveness of Ruscus aculetus extract combined or not with ascorbic acid (AA) and hesperidine methyl chalcone (HMC) on ischemia reperfusion (I/R) injury protection, little is known about the contribution of each constituent for this effect.

OBJECTIVE

To investigate the effects of AA and HMC combined or not with Ruscus extract on increased macromolecular permeability and leukocyte-endothelium interaction induced by I/R injury.

METHODS

Hamsters were treated daily during two weeks with filtered water (placebo), AA (33, 100 and 300 mg/kg/day) and HMC (50, 150 and 450 mg/kg/day) combined or not with Ruscus extract (50, 150 and 450 mg/kg/day). On the day of experiment, the cheek pouch microcirculation underwent 30 min of ischemia, and the number of rolling and adherent leukocytes and leaky sites were evaluated before ischemia and during 45 min of reperfusion.

RESULTS

Ruscus extract combined with AA and HMC (Ruscus extract mixture) significantly prevented post-ischemic increase in leukocyte rolling and adhesion and macromolecular permeability compared to placebo and these effects were more prominent than AA and HMC alone on leukocyte adhesion and macromolecular leakage.

CONCLUSION

Ruscus extract mixture were more effective than its isolated constituents in protect the hamster cheek pouch microcirculation against I/R injury.

Effects of Ruscus extract on muscarinic receptors: Is there a role for endothelium derived relaxing factors on macromolecular permeability protection and microvascular diameter changes?

BACKGROUND

Protective effects of Ruscus extract on macromolecular permeability depend on its capacity to stimulate muscarinic receptors on endothelial cells and induce the release of endothelium derived relaxing factors (EDRFs).

OBJECTIVE

To investigate if these effects depend only on activation of muscarinic receptors or if EDRFs release are also necessary. We have also investigated the participation of Ruscus extract on muscarinic-induced release of EDRFs on microvascular diameters.

METHODS

Hamsters were treated daily during two weeks with Ruscus extract (50, 150 and 450 mg/kg/day) and then macromolecular permeability induced by histamine and arteriolar and venular diameters after cyclooxygenase (COX) and nitric oxide synthase (NOS) inhibitors: indomethacin and Nω-Nitro-L-arginine (LNA), respectively applied topically at 10-8M, 10-6M and 10-4M were observed on the cheek pouch preparation.

RESULTS

Ruscus extract decreased macromolecular permeability in a dose-dependent fashion and did not affect microvascular diameters. NOS and COX inhibitors enhanced its effect on microvascular permeability. NOS inhibition reduced arteriolar diameter and COX blocking decreased arteriolar and venular diameters at the lowest dose and increased them at higher doses of Ruscus extract.

CONCLUSION

The protective effect of Ruscus extract on macromolecular permeability seems to be mediated only via muscarinic receptors. Muscarinic activation attenuated vasoconstrictive tone through cyclooxygenase-independent endothelium derived relaxing factors.

Chronic aerobic exercise associated to dietary modification improve endothelial function and eNOS expression in high fat fed hamsters

Obesity is epidemic in the western world and central adipose tissue deposition points to increased cardiovascular morbidity and mortality, independently of any association between obesity and other cardiovascular risk factors. Physical exercise has been used as non-pharmacological treatment to significantly reverse/attenuate obesity comorbidities. In this study we have investigated effects of exercise and/or dietary modification on microcirculatory function, body composition, serum glucose, iNOS and eNOS expression on 120 male hamsters treated for 12 weeks with high fat chow (HF, n = 30) starting on the 21st day of birth. From week 12 to 20, animals were randomly separated in HF (no treatment change), return to standard chow (HFSC, n = 30), high fat chow associated to an aerobic exercise training program (AET) (HFEX, n = 30) and return to standard chow+AET (HFSCEX, n = 30). Microvascular reactivity in response to acetylcholine and sodium nitroprusside and macromolecular permeability increase induced by 30 minutes ischemia followed by reperfusion were assessed on the cheek pouch preparation. Total body fat and aorta eNOS and iNOS expression by immunoblotting assay were evaluated on the experimental day. Compared to HFSC and HFSCEX groups, HF and HFEX ones presented increased visceral fat [(mean±SEM) (HF)4.9±1.5 g and (HFEX)4.7±0.9 g vs. (HFSC)*3.0±0.7 g and (HFSCEX)*1.9±0.4 g/100 g BW]; impaired endothelial-dependent vasodilatation [Ach 10(-8) M (HF)87.9±2.7%; (HFSC)*116.7±5.9%; (HFEX)*109.1±4.6%; (HFSCEX)*105±2.8%; Ach10(-6) M (HF)95.3±3.1%; (HFSC)*126±6.2%; (HFEX)*122.5±2.8%; (HFSCEX)*118.1±4.3% and Ach10(-4) M (HF)109.5±4.8%; (HFSC)*149.6±6.6%; (HFEX)*143.5±5.4% and (HFSCEX)*139.4±5.2%], macromolecular permeability increase after ischemia/reperfusion [(HF)40.5±4.2; (HFSC)*19.0±1.6; (HFEX)*18.6±2.1 and (HFSCEX)* 21.5±3.7 leaks/cm2), decreased eNOS expression, increased leptin and glycaemic levels. Endothelial-independent microvascular reactivity was similar between groups, suggesting that only endothelial damage had occurred. Our results indicate that an aerobic routine and/or dietary modification may cause significant improvements to high fat fed animals, diminishing visceral depots, increasing eNOS expression and reducing microcirculatory dysfunction.

Preconditioning of the response to ischemia/ reperfusion-induced plasma leakage in hamster cheek pouch microcirculation

OBJECTIVE

Ischemic preconditioning and some drugs can protect tissues from injury by preserving microcirculation. This study evaluated vascular permeability in a hamster cheek pouch preparation using either short ischemic periods or bradykinin as preconditioning stimuli followed by 30 min of ischemia/reperfusion.

METHOD

Sixty-six male hamsters were divided into 11 groups: five combinations of different ischemic frequencies and durations (one, three or five shorts periods of ischemia, separated by one or five minutes) with 10 min intervals between the ischemic periods, followed by 30 min ischemia/reperfusion; three or five 1 min ischemic periods with 10 min intervals between them followed by the topical application of histamine (2 µM); bradykinin (400 nM) followed by 30 min of ischemia/reperfusion; and three control groups (30 min of ischemia/reperfusion or histamine or bradykinin by themselves). Macromolecular permeability was assessed by injection of fluorescein-labeled dextran (FITC-dextran, MW= 150 kDa; 250 mg/Kg body weight), and the number of leaks/cm2 was counted using an intravital microscope and fluorescent light in the cheek pouch.

RESULTS

Plasma leakage (number of leaks/cm²) was significantly reduced by preconditioning with three and five 1 min ischemic periods, one and three 5 min ischemic periods and by bradykinin. Histamine-induced macromolecular permeability was also reduced after three periods of 5 min of ischemia.

CONCLUSION

Short ischemic periods and bradykinin can function as preconditioning stimuli of the ischemia/reperfusion response in the hamster cheek pouch microcirculation. Short ischemic periods also reduced histamineinduced macromolecular permeability.

MICRONIZATION ENHANCES THE PROTECTIVE EFFECT OF PURIFIED FLAVONOID FRACTION AGAINST POSTISCHAEMIC MICROVASCULAR INJURY IN THE HAMSTER CHEEK POUCH

1. The present study was designed to evaluate the effect of micronization on the protective effect of the purified flavonoid fraction (MPFF) on increases in macromolecular permeability induced by ischaemia-reperfusion in the hamster cheek pouch microcirculation. 2. Male hamsters (Mesocricetus auratus) were treated orally, twice a day, with vehicle (lactose), MPFF and non-micronized purified flavonoid fraction (PFF) at 5, 20, 80 and 320 mg/kg per day for 10 consecutive days. On the 11th day, cheek pouches of anaesthetized animals were prepared for intravital microscopy. 3. Local ischaemia was obtained by clamping the neck of the everted pouch and the increase in microvascular permeability was quantified as leakage (leaks) of intravenously injected fluorescein isothiocyanate-labelled dextran (FITC-dextran 150; MW = 150 000). 4. Reperfusion, after 30 min ischaemia, resulted in an immediate but reversible increase in post-capillary leakage. The MPFF induced a significant dose-related reduction in the increased permeability, with 83.4% inhibition compared with control at 320 mg/kg per day (19.2 +/- 1.9 vs 115.7 +/- 4.1 leaks/cm2; P < 0.0001). Non-micronized PFF was significantly less effective: only 47.9% inhibition compared with control was observed at 320 mg/kg per day (60.3 +/- 1.0 vs 115.7 +/- 4.1 leaks/cm2; P < 0.0001) and there was no dose-effect relationship. 5. In conclusion, micronization significantly enhances the protective effects of the purified flavonoid fraction on reperfusion injury in the hamster cheek pouch. This improvement is likely to be related to the better absorption of the micronized formulation, which could explain the superior clinical efficacy shown in previous studies.

Effects of sulfonylureas on K(ATP) channel-dependent vasodilation

INTRODUCTION

Sulfonylureas are widely prescribed for the treatment of type 2 diabetes. Their therapeutic efficacy resides in the ability to bind to sulfonylurea receptors (SURs) present on the beta-cell plasma membrane, to close the ATP-regulated potassium (K(ATP)) channel, and thereby to enhance glucose-stimulated insulin secretion. These receptors are also found in a wide variety of extra-pancreatic tissues such as brain, peripheral nerves, heart, and vascular smooth muscle where they contribute to the regulation of the vascular tone.

OBJECTIVE

The objective of the present study was to determine the potency of three sulfonylureas, glibenclamide, gliclazide, and glimepiride, in antagonizing the vasorelaxant action of diazoxide, an ATP-regulated K(+) channel (K(ATP)) opener, in vivo, using the hamster cheek pouch preparation and evaluating the changes in mean internal diameter and blood flow of arterioles and venules.

MATERIAL AND METHODS

Cheek pouches of anesthetized male hamsters superfused with a HEPES-supported HCO(3)(-)-buffered saline solution were placed under an intravital microscope coupled to a closed-circuit TV system. All substances were applied topically.

MEASUREMENTS

Mean arteriolar and venular internal diameters using an image shearing device, red blood cell (RBC) velocity by the dual-slit photometric technique and microvessel volume flow was calculated from diameters and RBC velocities.

RESULTS

The numbers are given in order, first diameter and then flow, always for the highest concentration of diazoxide tested, by itself or in combination with a given sulfonylurea: (1) diazoxide, used in doses of 0.01, 1, and 100 microM, elicited a dose-dependent dilation and flow increase in arterioles [increase of 52.1% (P<.01) and 41.2% (P<.01)] and venules [37.9% (P<.05) and 57.6% (P<.01)]; (2) glibenclamide (0.81 microM)+diazoxide 29.3% (P=.172) and 25.0% (P=.064) for arterioles and 8% (P=.654) and 3.7% (P=.769) for venules; (3) gliclazide (12 microM)+diazoxide 51.0% (P<.01) and 46.7% (P<.01) for arterioles and 59.0% (P<.01) and 45.2% (P<.01) for venules; (4) glimepiride (0.82 microM)+diazoxide 22.8% (P=.228) and 12.5% (P=.305) for arterioles and 15.6% (P=.415) and 16.0% (P=.291) for venules.

CONCLUSION

These results suggest that, in contrast to glibenclamide and glimepiride, therapeutic concentrations of gliclazide produce no cross-reactivity with smooth muscle cell K(ATP) channels in the microvessels of the hamster cheek pouch. Previous studies have confirmed these results in isolated aortic rings of rats and guinea pigs.

Antithrombin effects on endotoxin-induced microcirculatory disorders are mediated mainly by its interaction with microvascular endothelium

OBJECTIVE

To investigate whether the protective effect of antithrombin III, which has been shown to exert beneficial effects during septic disorders, including reduction of endotoxin-associated leukocyte/endothelial cell interaction and capillary perfusion failure, is mainly based on its anticoagulant capacity or direct effects on the microvascular endothelium.

DESIGN

Animal study with three treatment groups.

SETTING

Animal research facility.

SUBJECTS

Syrian golden hamsters, 6-8 wks old with a body weight of 60-80 g.

INTERVENTIONS

In skinfold preparations of hamsters, normotensive endotoxemia was induced by intravenous administration of 2 mg/kg endotoxin (lipopolysaccharide, 2 mg/kg). Antithrombin III (n = 7 animals; 250 units/kg) or tryptophan49-blocked antithrombin III (n = 6; 250 units/kg) was substituted intravenously 5 mins before lipopolysaccharide administration. Saline-treated animals (n = 11), receiving only lipopolysaccharide, served as controls. Tryptophan49-blocked antithrombin III binds to glycosaminoglycans at the endothelial surface to a significantly lower extent while retaining its progressive anticoagulant effects.

MEASUREMENTS AND MAIN RESULTS

Compared with controls, antithrombin III significantly reduced lipopolysaccharide-induced arteriolar and venular leukocyte adherence (p < .01) and prevented depression of functional capillary density (p < .01), whereas tryptophan49-blocked antithrombin III failed to significantly improve both variables. As measured in vivo by a monoclonal fluorescein isothiocyanate-labeled anti-antithrombin III antibody and intravital microscopy, the lack of effect of tryptophan49-blocked antithrombin III was associated with significantly lower antithrombin III/endothelium binding coefficients after 1 hr, 3 hrs, and 24 hrs of endotoxemia (p < .01).

CONCLUSIONS

We conclude that specific antithrombin III interactions with cell-surface glycosaminoglycans on the endothelium rather than anticoagulant properties are the mechanism of antithrombin III-mediated attenuation of leukocyte/endothelial cell interaction and capillary perfusion failure.

Vascular endothelial growth factor and the in vivo increase in plasma extravasation in the hamster cheek pouch

1. The purpose of this study in the hamster cheek pouch was to determine whether or not vascular endothelial growth factor (VEGF) induced changes in plasma extravasation and if so, the mechanism(s) involved. 2. The cheek pouch microcirculatory bed of the anaesthetized hamster was directly observed under microscope and the number of vascular leakage sites, as shown by fluorescein isothiocyanate (FITC-dextran, 150 kD) extravasation, was counted. Drugs and VEGF were applied topically. VEGF from 0.05 to 0.5 microg ml(-1) (1.2 to 12 nM) produced a dose-dependent increase in the number of microvascular leakage sites from virtually none in basal conditions to up to 250 in some pouches. The effects of VEGF (0.1 microg ml(-1) or 2.4 nM) were blocked in a concentration-dependent manner by the non-specific heparin growth factor antagonist TBC-1635 (0.1, 1 and 3microM). The placenta growth factor (PlGF-1: 0.1 and 0.5 microg ml(-1) or 3.4 and 17 nM) did not increase plasma extravasation, per se, but abolished the effects of VEGF (2.4 nM). 3. The increases in microvascular leakage produced by VEGF (2.4 nM) were partially but significantly (P<0.05) inhibited by genistein (5 and 10 microM, up to 33% inhibition), LY 294002 (30 microM, 41%), bisindolylmaleimide (1 microM, 65%) and virtually abolished by indomethacin (3 microM, 88%) and L-nitro-arginine (10 microM, 95%), these drugs being inhibitors of tyrosine kinase, phosphatidylinositol-3-kinase, protein kinase C, cyclo-oxygenase and nitric oxide synthase respectively. None of these inhibitors, at the concentration tested, induced alone an increase in plasma extravasation. 4. These results indicate that the VEGF-induced plasma extravasation may involve the stimulation of VEGF-R2 (Flk-1/KDR) and the activation of phosphatidylinositol-3-kinase and protein kinase C. The production of both nitric oxide and prostaglandin is required to observe an increase in vascular leakage.

Determination of macromolecular exchange and PO2 in the microcirculation: a simple system for in vivo fluorescence and phosphorescence videomicroscopy

We have developed a system with two epi-illumination sources, a DC-regulated lamp for transillumination and mechanical switches for rapid shift of illumination and detection of defined areas (250-750 microm(2)) by fluorescence and phosphorescence videomicroscopy. The system permits investigation of standard microvascular parameters, vascular permeability as well as intra- and extravascular PO2 by phosphorescence quenching of Pd-meso-tetra (4-carboxyphenyl) porphine (PORPH). A Pechan prism was used to position a defined region over the photomultiplier and TV camera. In order to validate the system for in vivo use, in vitro tests were performed with probes at concentrations that can be found in microvascular studies. Extensive in vitro evaluations were performed by filling glass capillaries with solutions of various concentrations of FITC-dextran (diluted in blood and in saline) mixed with different amounts of PORPH. Fluorescence intensity and phosphorescence decay were determined for each mixture. FITC-dextran solutions without PORPH and PORPH solutions without FITC-dextran were used as references. Phosphorescence decay curves were relatively unaffected by the presence of FITC-dextran at all concentrations tested (0.1 microg/ml to 5 mg/ml). Likewise, fluorescence determinations were performed in the presence of PORPH (0.05 to 0.5 mg/ml). The system was successfully used to study macromolecular extravasation and PO2 in the rat mesentery circulation under controlled conditions and during ischemia-reperfusion.

Microvascular permeability with sulfonylureas in normal and diabetic hamsters

The hamster cheek pouch is an experimental model in which quantitative studies of macromolecular permeability can be made by direct observation of extravasated fluorescein isothiocyanate (FITC)-dextran (leaks). The advantage of this model is that simultaneous light and fluorescent-light microscopy observations can be performed with instantaneous correlations between the site of FITC-dextran extravasation and the vessel morphology. The aims of our study were to compare, using the cheek pouch preparation, the effects of two sulfonylureas, gliclazide and glibenclamide, on the macromolecular permeability increase induced by histamine using control (normoglycemic) hamsters. In these studies, FITC-labeled dextran 150,000 daltons was administered intravenously and quantified by UV-light microscopy, and the drugs used were applied topically at therapeutic concentrations. Gliclazide and glibenclamide dose-dependently decreased the macromolecular permeability increase induced by histamine. This effect of gliclazide could be blocked by nifedipine (Ca2+ channel blocker) and not by diazoxide (K+ channel opener), whereas for glibenclamide it could be blocked by diazoxide and not by nifedipine. To better characterize the antioxidant capacity of gliclazide and glibenclamide, their effect on the macromolecular permeability increase induced by ischemia/reperfusion was also compared with the effect of vitamin C in diabetic hamsters (glycemia > 240 mg/dL). Total ischemia of the preparation was obtained with a cuff placed around the neck of the everted pouch. Diabetes was induced by three intraperitoneal injections of streptozotocin 50 mg/kg/d in 3 days. In diabetic hamsters during ischemia/reperfusion, gliclazide was more effective in inhibiting the macromolecular permeability increase than glibenclamide (136.0 +/- 5.8 leaks/cm2 for placebo; 68.0 +/- 2.9 for 1.2 x 10(-6) mol/L gliclazide; 55.3 +/- 3.5 for 1.2 x 10(-5) mol/L gliclazide; 89.2 +/- 5.7 for 8 x 10(-8) mol/L glibenclamide; 107.0 +/- 3.8 for 8 x 10(-7) mol/L glibenclamide; 56.7 +/- 3.4 for 10(-6) mol/L vitamin C; and 20.5 +/- 0.6 for 10(-5) mol/L vitamin C). Our results suggest that (1) the inhibition of the permeability increase induced by histamine elicited by gliclazide may be mediated by Ca2+ channels, while that of glibenclamide may be mediated by K+ channels, and (2) gliclazide appears to have an antioxidant capacity in ischemia/reperfusion injury similar to that of 10(-6) mol/L vitamin C. Improvement in the microcirculation was independent of the hypoglycemic properties of the drug.

Effects of oral administration of purified micronized flavonoid fraction on increased microvascular permeability induced by various agents and on ischemia/reperfusion in the hamster cheek pouch

The effects of a clinically used purified micronized flavonoid fraction (S 5682) containing 90% diosmin and 10% hesperidin on increased microvascular permeability induced by histamine, bradykinin, and leukotriene B4 (LTB4) were investigated by intravital microscopy in the hamster cheek pouch preparation. The authors also investigated the effects of S 5682 on macromolecular permeability increase and leukocyte adhesion during ischemia-reperfusion by using the same preparation. S 5682, suspended in 10% lactose solution, or vehicle (10% lactose) was administered orally to male hamsters for ten days at 20 mg/kg/day (10 mg/kg twice a day). Fluorescein isothiocyanate (FITC)-labeled dextran (mol wt 150,000) was given intravenously, thirty minutes after completion of the cheek pouch preparation. The leukocytes were stained by continuous IV infusion of acridine orange (0.5 mg/kg/minute). Histamine (2 microM), bradykinin (1 microM), and LTB4 (0.01 microM), applied topically for five minutes, increased the number of fluorescent vascular leakage sites in postcapillary venules. A temporary ischemia with total circulatory arrest of the cheek pouch was obtained by clamping the neck of the everted pouch. The maximum number of leaky sites (per cm2 in the prepared area) that occurred either at five minutes after the beginning of each topical application or ten minutes after the onset of reperfusion was quantified in ultraviolet light microscopy. The results from 60 animals divided into 10 groups of 6 animals each are presented as means +/- SEM. In comparison with vehicle, S 5682 significantly inhibited the macromolecular permeability increasing effect of histamine (343.5 +/- 22.3 versus 207.5 +/- 32.0 leaks/cm2; P < 0.01), bradykinin (345.2 +/- 19.0 versus 206.2 +/- 21.6 leaks/cm2; P < 0.01), and LTB4 (353.3 +/- 27.5 versus 242.7 +/- 33.6 leaks/cm2; P < 0.05). At reperfusion, after thirty minutes of ischemia, S 5682 significantly decreased the observed macromolecular permeability (103.6 +/- 15.4 versus 42.6 +/- 9.3 leaks/cm2; P < 0.01). Flavonoid-treated animals also displayed a statistically significant lower number of adhering leukocytes to the venular endothelium (83.5 +/- 9.5 versus 48.4 +/- 12.3 per 6 mm2; P < 0.05). These results demonstrate that oral administration of S 5682 for ten days at 20 mg/kg body weight/day had a protective effect against leakage of macromolecules after application of permeability-increasing substances and during ischemia-reperfusion in the cheek pouch microvasculature. Since firm leukocyte attachment to the endothelial wall and subsequent emigration of leukocytes into the interstitium is a mechanism for tissue damage during inflammation, attenuation of this phenomenon during conditions of ischemia-reperfusion can in part explain previous observations that this purified micronized flavonoid fraction decreases edema formation. The present data illustrating the inhibitory effect of a clinically relevant dose of S 5682 on the inflammatory processes induced in this in vivo model of microcirculation may serve as a rational basis to explain its clinical efficacy.

Microvascular reactivity after ischemia/reperfusion in the hamster cheek pouch: beneficial effects of different oral doses of S-5682 (Daflon 500 mg)

Daflon 500 mg (S-5682) is a purified, micronized flavonoid fraction containing 90% diosmin and 10% hesperidin that is currently used to treat chronic venous insufficiency and hemorrhoidal disease. Thus, it seemed of interest to evaluate the effects of S-5682 on ischemia/reperfusion, ie, the changes in mean internal diameter and blood flow of arterioles and venules and the functional capillary density (FCD) during reperfusion after ninety minutes of total ischemia in the hamster cheek pouch microvasculature. Different doses of S-5682 (5, 20, 80, and 160 mg/kg body weight/day), suspended in 10% lactose solution or vehicle (10% lactose) were administered orally to male hamsters for ten days twice a day. The cheek pouch preparation was placed under an intravital microscope coupled to a closed-circuit TV system. A ninety-minute local ischemia was obtained by a cuff mounted around the neck of the everted pouch where it left the mouth of the hamster. Mean arteriolar and venular internal diameters were determined by means of an image-shearing device, IPM model 907; red blood cell (RBC) velocity was measured by the dual-slit photometric technique; microvessel volume flow was calculated from diameters and RBC velocities; and FCD was defined as the number of red-cell-perfused capillaries per observation field. During reperfusion, placebo-treated animals showed significant vasodilatation concomitant with a decrease in blood flow and FCD compared with preischemic values and an impairment of the myogenic response. In S-5682-treated animals, there was a significant dose-dependent improvement in all these parameters including the myogenic tonus. These results clearly demonstrated that oral administration of different doses of S-5682 for ten days improved the microvascular reactivity and FCD after ischemia/reperfusion in a dose-dependent fashion in the hamster cheek pouch microvasculature.

Bradykinin and changes in microvascular permeability in the hamster cheek pouch: role of nitric oxide

1. The objective of this study in the hamster cheek pouch was to investigate the role of nitric oxide in bradykinin-induced microvascular leakage. The cheek pouch microcirculatory bed of the anaesthetized hamster was directly observed under microscope and vascular leakage was evidenced by dextranfluorescein isothiocyanate (FITC-dextran) extravasation. 2. Bradykinin superfusion (but not [des-Arg9]-bradykinin up to 3 x 10(-6) M) induced an increase in microvascular permeability (log EC50: -6.5 +/- 0.4) which was exclusively located on the post-capillary venule. Plasma extravasation was blocked by intravenous pretreatment with Hoe 140, a bradykinin B2 receptor antagonist (estimated log ID50: -9.5 +/- 0.2). 3. The effects of bradykinin (3 x 10(-7) M) superfusion were partially but significantly inhibited by indomethacin (10(-5) M, P < 0.05) and abolished by pretreatment with L-nitro-arginine (L-NOARG; 10(-5) M). 4. Acetylcholine (10(-6) M, which releases endothelial nitric oxide (NO), and sodium nitroprusside (10(-6) M, a nitrovasodilator) superfusion did not induce any changes in permeability, per se. Cromakalim (10(-5) M, a potassium channel opener) superfusion induced a moderate but significant plasma extravasation. 5. The effects of bradykinin, blocked by L-NOARG pretreatment, were restored by the co-perfusion of either sodium nitroprusside or cromakalim. Conversely vasoconstriction, produced by a stable analogue of thromboxane A2 (U46619, 3 x 10(-7) M), inhibited the increase in permeability produced by bradykinin. 6. The measurement of arteriolar diameter showed that bradykinin induced a vasodilatation which was blocked by L-NOARG. L-NOARG in itself was a powerful vasoconstrictor. Sodium nitroprusside and cromakalim, in the presence of L-NOARG, were able to restore the inhibited vasodilator response to bradykinin. 7. These results suggest: (1) bradykinin-induced microvascular leakage is mediated by bradykinin B2 receptor activation; (2) the increase in permeability is due to two different independent phenomena, i.e. post-capillary venular endothelial gap formation and arteriolar vasodilatation which increases the post-capillary venular transmural pressure: (3) NO is only involved in the arteriolar dilatation component of the bradykinin-induced increase in microvascular permeability.

Biological chemistry of thiols in the vasculature and in vascular-related disease

For all their similarities in structure and common chemistry, the functions of the amino thiols in vascular biology are remarkably different. This review details the basic chemistry of sulfhydryls that dictates their functions in health and disease. In addition, the biochemistry and metabolism of each thiol are outlined, in an effort to highlight its specific contributions to the normal biology and physiology of blood vessels and to the pathogenesis of vascular-related disease.

Plasma exudation and solute absorption across the airway mucosa

The airway mucosa responds to inflammatory provocations with bulk exudation of plasma into the airway tissue (vascular exudation) and lumen (mucosal exudation). The intensity and time course of the exudative response can be relevantly examined by sampling and analysing airway surface liquids, because the luminal entry of plasma proteins/tracers promptly and quantitatively reflects the exudative response of the airways. The process of mucosal exudation of plasma is a prominent feature of airway inflammation and has been demonstrated in rhinitis, asthma, and bronchitis. Inflammatory mediators and allergen produce mucosal exudation of plasma into the airway lumen (outward permeability) whereas the solute absorption across the mucosa (inward permeability) is unaffected. Hence, in contrast to current views, we have demonstrated that in airway inflammation the solute absorption across the airway mucosa is not increased. The findings suggest the plasma exudation response also as a first line respiratory mucosal defence, allowing potent plasma protein systems to appear on an airway mucosa functionally intact as a barrier toward undue luminal material. Our data on plasma exudation and solute absorption across the mucosa of upper and lower airways further suggest the human nasal airways as a model relevant also for the tracheobronchial airways.

Polycations induce microvascular leakage of macromolecules in hamster cheek pouch

The microvascular response to two polycationic proteins, poly-L-lysine (mol wt 104,000) and leukocyte elastase, was studied in the hamster cheek pouch microcirculation model. A 2-min topical application of polylysine (100 micrograms/ml) induced vigorous macromolecular leakage from venules only that declined within 30 min. A second application induced significantly less leakage. The leakage was inhibited by admixing polylysine with dextran sulfate prior to application or by giving hamsters an intravenous injection of dextran sulfate. The histamine antagonist pyrilamine did not interfere with the leakage, and only a few degranulated mast cells were found after polylysine application. No intravascular adhesion of leukocytes could be detected. Elastase (100 micrograms/ml) was deposited adjacent to venules with micropipets. The resulting leakage response was not inhibited by L658,758, an inhibitor of elastase enzymatic activity, but by dextran sulfate. These results may prove significant in light of the numerous polycationic proteins present within neutrophil granules.

Effects of hypertonic NaCl solution on microvascular haemodynamics in normo- and hypovolaemia

The aims of this study were to investigate possible resuscitation effects of a single, 10-min, 350-microliters intravenous infusion of 7.5% NaCl in hamsters in hemorrhagic shock and to compare the effects of such infusion with an identical one of 0.9% NaCl on the hamster cheek pouch microcirculation during normovolaemia and after acute bleeding to a hypotension level of about 40 mmHg. No significant differences could be detected between the effects of either infusion given to normovolaemic normotensive hamsters. In the animals subjected to haemorrhage, upon bleeding, arterioles larger than 40 microns constricted, arterioles smaller than 40 microns dilated and venular diameter did not change, while blood flow decreased in all vessels. The main differences between the infusions after haemorrhage were a significant increase in mean arterial pressure and arteriolar blood flow, venoconstriction and a tendency for the smaller arterioles to remain more dilated and the larger ones more constricted after the hypertonic infusion. Central nervous and/or reflex excitation of the sympathetic nervous system could account for the constriction of venules and larger arterioles, while a direct effect of hyperosmolarity could explain the dilatation of the smaller arterioles. The study can therefore help to explain some of the mechanisms underlying the reported resuscitation effect of 7.5% NaCl infusion in animals during severe haemorrhagic hypovolaemia.

Mechanisms of tumor-associated edema: a review

An understanding of the mechanisms responsible for tumor-associated edema involves the elucidation of the role played by a number of intra-related processes. These include (i) the permeability of new tumor microvessels that are associated with tumor angiogenesis; (ii) alterations in microvascular permeability due to factors secreted by tumor cells; (iii) immunological mechanisms and (iv) increased microvessel permeability associated with inflammation. The rationale for a role for inflammatory processes in tumor-associated edema has been outlined and the role of non-steroidal anti-inflammatory drugs in modulating experimental and human tumor-associated edema has been explored.

Vasodilatation and inhibition of mediator release represent two distinct mechanisms for prostaglandin modulation of acute mast cell-dependent inflammation

1. Intravital microscopy of the hamster cheek pouch was used to examine the influence of vasodilator prostanoids (prostaglandin E2 (PGE2), PGI2), forskolin, and nitroprusside on the microvascular changes during acute inflammation induced by antigen or histamine. The results extend our previous finding that PGE2 modulates allergic inflammation and histamine release in the cheek pouch model. 2. The microvascular actions of arachidonic acid and different cyclo-oxygenase products (PGE2, PGD2, PGI2, PGF2 alpha, and the thromboxane A2 (TXA2)-analogue U-44069) were first compared with respect to their effects on arteriolar tone. Of the prostaglandins, only PGE2 and PGI2 were potent vasodilators and markedly increased local blood flow. Nitroprusside and forskolin also caused vasodilatation and increased blood flow, but were somewhat less potent than PGE2 and PGI2. 3. Topically applied PGE2 and PGI2 in vasodilator concentrations suppressed the antigen-induced plasma leakage. On the other hand, although the antigen response was predominantly mediated by histamine, both prostaglandins enhanced the plasma leakage evoked by exogenous histamine. 4. In contrast, the vasodilator nitroprusside, in a dose causing an increase in blood flow equal to that of PGE2 and PGI2, potentiated both the histamine-induced plasma leakage, as well as the plasma and leukocyte extravasation after antigen challenge, indicating that the anti-inflammatory actions of the prostaglandins were unrelated to their vasodilator properties per se. 5. Because forskolin, a specific activator of adenylate cyclase, mimicked the actions of PGE2 and PGI2, i.e. inhibition of the antigen-induced plasma extravasation and enhancement of the histamine response, it is possible that the observed antiallergic effects of the prostaglandins were related to accumulation of intracellular adenosine 3': 5'-cyclic monophosphate (cyclic AMP). 6. Taken together, there appears to be a competition between pro- and anti-inflammatory effects of PGE2 and PGI2 in reactions involving release of endogeneous inflammatory mediators in vivo, i.e. enhancement of inflammatory mediator target action on one hand ('two mediator synergism'), and suppression of mediator release on the other. Moreover, the observations indicate that vasodilatation and inhibition of mediator release are two distinct actions of PGE2 and PGI2.

Intrathoracic microvascular circulation in haemorrhagically shocked rats. Studies by fluorescence techniques

The microvascular circulation in the heart, lung and thymus was studied by fluorometry in 32 haemorrhagically shocked rats. Exsanguination to a blood pressure of 35 mmHg for 180 min did not result in any reduction of this circulation in the heart or lung, but in the thymus it was reduced by 52%. Retransfusion of shed blood caused no change in cardiac microcirculation, whereas the microcirculation in the thymus was increased by 59%. In the lungs a heterogeneous fluorescence pattern was observed after retransfusion, with large dark areas alternating with normal fluorescent ones and even some small intensively fluorescent areas. After retransfusion, maldistribution of blood flow seems to be a phenomenon of haemorrhagic shock in the lungs.

Dextran sulfate prevents LTB4-induced permeability increase, but not neutrophil emigration, in the hamster cheek pouch

Leukotriene B4 (LTB4) is known to induce neutrophil-dependent macromolecular leakage in the hamster cheek pouch. LTB4 was superfused over cheek pouches dissected for intravital microscopy; and leukocyte rolling and firm adhesion in venules, neutrophil emigration, and macromolecular permeability as leakage of fluorescent dextran was quantified. Dextran sulfate (MW 500,000; 17.5 mg/kg iv bolus), but not uncharged dextran, reduced the LTB4-induced venular leakage of macromolecules by 85%. Histamine-induced leakage, which is neutrophil independent, was left unaffected. Dextran sulfate had no effect on leukocyte adhesion in postcapillary venules induced by LTB4, nor on their subsequent emigration to the surrounding tissue. Dextran sulfate significantly inhibited leukocyte rolling during nonstimulated conditions along the walls of collecting venules, but not postcapillary venules. Consequently, neutrophil-induced macromolecular leakage and neutrophil emigration appear to be independent, separable events. As an explanation of the present results it is proposed that the dextran sulfate complexes neutrophil granule cationic proteins, thus preventing neutrophil-mediated permeability increase.

Analysis of microvascular permeability to macromolecules by video-image digital processing

The dynamics of macromolecular transport across microvascular walls were studied in the hamster cheek pouch by intravital fluorescence microscopy. A graded series of fluorescein isothiocyanate-labeled dextrans (FITC-Dx) of 20,000-70,000 MW was used as macromolecular tracers. The time-dependent extravasation of FITC-Dxs was videotaped for about 2.5 hr to allow for tracer equilibration in the interstitial space. Permeation of macromolecules from individual microvessels was quantified by digital video-image processing. Histograms of the light intensity distributions for selected fields at various times were measured and used to construct integral optical density-time profiles of the extravasated fluorochromes for particular leaky sites. A nonlinear regression algorithm was employed to determine the effective microvascular permeability (P) for the macromolecules studied using a one-dimensional two-compartmental diffusion model and a step change in macromolecular concentration at the boundary. The calculated P's (X 10(-8) cm/sec) were 47.8 +/- 8.7 for FITC-Dx 20; 31.7 +/- 5.9 for FITC-Dx 40, and 17.5 +/- 4.1 for FITC-Dx 70. Our values are comparable to those obtained by whole organ techniques. The observed differences can be explained by explicit consideration of interstitial resistance in the calculations.

Prostaglandin E2 prevents diclofenac-induced enhancement of histamine release and inflammation evoked by in vivo challenge with compound 48/80 in the hamster cheek pouch

Based on observations obtained by the use of intravital microscopy, we report that prostaglandins (PGs) can exert inhibitory effects on mast cell-dependent inflammation. Thus, the PG-synthesis inhibitors diclofenac and indomethacin potentiated extravasation of plasma evoked by challenge with the mast cell secretagogue compound 48/80. Although the plasma leakage induced by compound 48/80 was in large mediated by histamine, neither diclofenac nor indomethacin potentiated the plasma leakage caused by exogenous histamine. These findings indicated that endogenous PGs inhibited the mast cell-dependent reaction at the level of mediator release. This mode of action was confirmed, as diclofenac was found to enhance the in vivo release of histamine that ensued challenge with compound 48/80. Moreover, the enhancement of the response to compound 48/80 observed after diclofenac treatment was prevented by local administration of PGE2 (30 nM). This inhibition included both the histamine release and the plasma leakage. In addition, diclofenac enhanced the leukocyte emigration after compound 48/80 challenge, and PGE2 reversed also this effect, suggesting that endogenous PGs (e.g. PGE2) also inhibited the release of chemotactic mediators.

An intravital microscopic model for mast cell-dependent inflammation in the hamster cheek pouch

Topical antigen challenge in cheek pouches of immunized hamsters led to an acute inflammatory reaction which was characterized by intravital microscopy. The response consisted of short-lasting arteriolar spasm, followed by leakage of plasma, vasodilation, and accumulation of leucocytes. Several observations indicated that the reaction was due to mast cell activation. Thus, a very similar inflammatory response was seen after challenge with compound 48/80, and both antigen and compound 48/80 degranulated the numerous mast cells present in the cheek pouch. In addition, fluorescein-labelled antigen bound specifically to mast cells in cheek pouches of immunized animals, also suggesting the presence of mast cell-fixed antigen-specific antibodies, possibly immunoglobulin E. However, although antigen and compound 48/80 caused similar microvascular responses, cross-desensitization experiments indicated that the two stimuli activated mast cells via different mechanisms. The histamine antagonist mepyramine, which abolished plasma leakage induced by exogenous histamine, substantially inhibited the increase of microvascular permeability evoked by antigen or compound 48/80, but did not appear to affect the vasospasm and leucocyte accumulation. It is concluded that the hamster cheek pouch may be a most useful tool for investigation of dynamic microvascular events during allergic mast cell-dependent inflammation.

Acute microvascular effects of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine: comparisons with leukotriene B4

Acute effects of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) on microvessels of the hamster cheek pouch were studied using intravital and electron microscopy. FMLP (1.0 microM) applied topically to the pouch microvasculature produced transient vasoconstriction of second- and third-order arterioles, which was accompanied by modest narrowing of pericytic venules, leukocyte adherence, diapedesis, and macromolecular extravasation. Contrary to observations of leukotriene B4 (LTB4)-exposed venules in the same animal model, electron micrographs of fMLP-treated venules supported junctional, vesicular, and potential transcellular modes of transendothelial protein transport. Endothelial junctions were not characterized by large gaps, but failure of endothelial processes to effectively bridge diapedesing cells and reestablish junctional contact resulted in substantial deposition of subendothelial reaction product. Venous microvessels 18-21 micron in diameter were particularly susceptible to the deleterious effects of fMLP and revealed the highest percentage of total junctions or endothelial cells labeled by reaction product. Implied barrier dysfunction was more prevalent in fMLP-treated vessels exhibiting adherence and/or diapedesis; however, the presence of barrier defects was not correlated with leukocyte margination and/or emigration (Marg/Emig). The absence of simple correlation, without persuasive evidence for direct vasopermeability effects, recognizes that some Marg/Emig events may not have been present at the time of fixation and suggests the potential for neutrophil-mediated endothelial dysfunction, governed by multiple determinants, is often unrealized.

False-positive artifacts of tracer strategies distort autonomic connectivity maps

The widespread use of new axonal transport tracing techniques in the ANS has resulted in substantially revised and amended descriptions of ANS organization. The present review suggests, however, that at least some of the results on which proposed revisions of ANS anatomy have been based have incorporated artifacts and therefore should be cautiously interpreted. The peripheral nervous system and viscera are composed in part of connective and endothelial tissues that are porous or 'leaky' to solutes with appropriate chemical characteristics, including the major tracer compounds. As a result, several extra-axonal routes for redistribution of label from the application site into other tissues are present. These include (1) diffusion through tissue membranes to enter directly adjacent tissues and (2) leakage into extracellular fluids within the body cavity, vasculature, lymphatics, exocrine ducts, or organ lumens to migrate to more distant tissues. As a consequence of the extreme sensitivity of the methods used, such redistribution of even minute amounts of label can produce false positives. Review of autonomic neuroanatomy suggests additional mechanisms, including tracer uptake by fibers of passage, can produce artifactual staining. Based on these surveys of tissue composition, tracer characteristics and sources of artifact, experimental controls and criteria for identifying and avoiding labeling artifacts are described. Since no single procedure is foolproof for ANS experimentation, the routine application of multiple controls, particularly ones which restrict or prevent tracer diffusion, are needed.

Enhancement of acute allergic inflammation by indomethacin is reversed by prostaglandin E2: apparent correlation with in vivo modulation of mediator release

Intravital microscopy and determination of in vivo histamine release revealed that the cyclooxygenase inhibitor indomethacin reduced antigen-induced vasodilation while enhancing plasma extravasation, leukocyte accumulation, and histamine release in cheek pouches of immunized hamsters. Topical application of prostaglandin E2 (PGE2, 30 nM) totally reversed the indomethacin-induced potentiation of the inflammatory reaction to antigen challenge and suppressed both the histamine release and plasma leakage also in the absence of indomethacin. On the other hand, PGE2, which per se caused vasodilation, markedly potentiated the postcapillary leakage of plasma induced by histamine or leukotriene C4, as well as the leukocyte activation and subsequent plasma extravasation evoked by leukotriene B4. Taken together, the data indicate that PGE2 reduced the antigen response by suppression of mediator release from the numerous mast cells present in the cheek pouch. Moreover, the PGE2-sensitive potentiation by indomethacin of the antigen response suggests that endogenous vasodilating prostaglandins (possibly PGE2) predominantly were anti-inflammatory.

The effects of steroidal and nonsteroidal anti-inflammatory agents on uptake of Evans blue in experimental metastasis

The effects of anti-inflammatory drugs on uptake of Evans blue were studied in solitary Walker carcinosarcomas implanted in the livers of Sprague-Dawley rats. Animals were sacrificed at 5 min, 30 min, and 6 hr after administration of the anti-inflammatory drugs and Evans blue, and spectrophotometric measurements of the Evans blue in tumor and normal liver tissue were carried out. Uptake of Evans blue in the tumors was significantly decreased at all time periods after the injection of the following, as compared to controls: steroids (cortisol, methylprednisolone, and triamcinolone), the antihistamine diphenhydramine, and nonsteroidal anti-inflammatory agents (naproxen, ibuprofen, indomethacin, and phenylbutazone). The effects of these drugs on uptake of Evans blue in the normal liver were more variable.

Disturbance of peripheral microcirculation by LHRH-agonists. II

It could be demonstrated with the aid of a cheek pouch model of the hamster that the LHRH-agonist lutrelin (Wyeth, WY 40972) caused disturbances of microcirculation within minutes, for example constriction of the arterioles and venules, reduction in capillary density and increased permeability, effects which were not reversible within the observation period (1 h) and could not be antagonized by the cyclooxygenase inhibitor indomethacin. Likewise, the lutrelin-induced accumulation of leucocytes in the capillaries of the testes of the rat could not be prevented within 6 hours after administration of indomethacin, whereas the harmful effect of lutrelin on the germinal epithelium could be antagonized by indomethacin within 24 hours. A biphasal course is assumed, characterised by an acute non-prostaglandin-dependent phase and a second prostaglandin-dependent phase, which causes the definitive damage to the testis of the rat.

Diapedesis and the permeability of venous microvessels to protein macromolecules: the impact of leukotriene B4 (LTB4)

The cellular basis of the reported neutrophil-dependent increase in microvascular permeability evoked by leukotriene B4 (LTB4) was probed using protein intravascular fluorescent and electron dense tracers in conjunction with intravital, light and electron microscopy. LTB4 (1 microM) applied topically to the hamster cheek pouch promoted neutrophil (PMN) adherence to endothelial cells (ECs) and resulted in limited, diffuse leakage of fluorescein-labeled albumin from pericytic venules. ECs to which PMNs adhered displayed many vesicles and a prominent cytoskeletal reorganization of microfilaments. During emigration, microfilament-rich luminal extensions of ECs effectively resealed the endothelial barrier prior to or in conjunction with PMN penetration of the basal lamina. Intimate associations between PMNs and ECs, coupled with efficient bridging of the lumen by EC processes, argued against significant transendothelial escape of macromolecules concomitant with PMN egress. Studies employing horseradish peroxidase as an intravascular tracer suggested minimal enhancement of junctional permeability in small venules and refuted a role for vesicular transport. The primary apparent barrier defect was a selective alteration in the membrane integrity of a proportion of ECs.

Action of the stable prostacyclin analogue iloprost on microvascular tone and -permeability in the hamster cheek pouch

In order to further elucidate the mechanisms involved in therapeutic effects of prostacyclin and Iloprost in peripheral ischemic disease, the actions on microvascular tone, capillary density, and increases in venular permeability induced by inflammatory mediators and by ischemia were investigated in the cheek pouch of anaesthetized Syrian hamsters using intravital videomicroscopy and--for quantification of vascular permeability--venular leakage of fluorescein-labelled dextran (FITC-D; Mw 70,000). Iloprost at the nonhypotensive, platelet aggregation-inhibiting dose of 0.5 microgram/kg/min i.v. significantly increased the diameters of arterioles and venules and the density of perfused capillaries and antagonized vasoconstriction and decrease of perfused capillary density as induced by Leukotriene D4 (LTD4; 10(-7) M). Iloprost significantly antagonized venular leakage of FITC-D induced by histamine (10(-5) M), serotonin (10(-5) M), bradykinin (10(-6) M) and reperfusion after 30 min ischemia. Topical application of Iloprost (10(-8) M), intraarterial infusion of Prostaglandin E1 (PGE1; 2.0 micrograms/kg/min), and topical Forskolin (10(-5) M) also attenuated histamine-induced venular FITC-D leakage, while topical PGE1 (10(-7) M) and i.v. infusion of Nifedipine (30 micrograms/kg + 10 micrograms/kg/min) were not effective. It is concluded, that microvascular effects of Iloprost by improvement of tissue perfusion and functional antagonism of mediator-induced tissue edema and vasospasm could contribute to therapeutic effectiveness in ischemic diseases.

Quantitation of bradykinin-induced microvascular leakage of FITC-dextran in rat cremaster muscle

We studied the in vivo effects of bradykinin (BK) on transvascular movement of macromolecules in the rat cremaster muscle. The muscle was fashioned as a single layer, placed in a transparent chamber, and superfused with a bicarbonate buffer solution (pH 7.4, 35 degrees). FITC-Dextran 150 (MW 150,000) was injected iv as a macromolecular tracer. The fluorescent tracer remained in the vascular compartment during control observations. BK (8 X 10(-8) to 8 X 10(-7) M) was topically applied for periods of 5 min. Depending on the dose, leakage of FITC-Dextran 150 started 2-3 min after the application of BK. Discrete leakage sites were detected for a short period at the beginning of the response only. Subsequently, the entire interstitial space became fluorescent as the leakage lasted for several minutes. The preparation returned to control appearance after 40-60 min of continuous superfusion with bicarbonate buffer. Macromolecular leakage was observed in postcapillary venules ranging from 15 to 50 microns in diameter. Neither arterioles nor true capillaries showed leakage of the tracer. To better quantitate the effect of BK on macromolecular transport, the superfusate output was collected at 5-min intervals and analyzed by fluorometry to determine FITC-Dextran 150 concentration. After BK, fluorochrome concentration in the superfusate rose, peaked by 15-20 min, and returned to control levels following 60 min of washout. A direct dose-response relationship was found between BK concentration and clearance of FITC-Dextran 150. These data demonstrate the feasibility of quantitatively studying blood-tissue transport of macromolecules in vivo in skeletal muscle.

Terbutaline and budesonide as inhibitors of postischaemic permeability increase

A temporary ischaemia with total circulatory arrest of the hamster cheek pouch was obtained by clamping the neck of the everted cheek pouch. The macromolecular permeability increase in postcapillary venules was quantified as the leakage of fluorescein-labelled dextran using intravital microscopy and a fluorometer simultaneously. At reperfusion after 30 min ischaemia, there was a significant and reversible permeability increase. This response could be totally prevented by topical administration of either terbutaline, a selective beta 2-receptor agonist, or budesonide, a glucocorticoid, but it was not significantly impeded by the antihistamine mepyramine. The study shows that, in conformity with the situation in inflammation, the postischaemic permeability increase at reperfusion after ischaemia can be blocked by either beta 2-stimulation or glucocorticoids. Furthermore, it indicates that histamine, a common inflammatory mediator, is not responsible for the postischaemic permeability increase.

Immune-complex-induced inflammatory reaction studied by intravital microscopy: role of histamine and arachidonic acid metabolites

An immune-complex-induced inflammatory reaction was elicited in the hamster cheek pouch microvasculature of ovalbumin (OA)-immunized animals by exposure to 1 or 100 micrograms/ml OA. The low antigen dose caused arteriolar constriction, transient platelet aggregation, and a reversible increase in vascular leakage at postcapillary venules. With the high antigen dose, the constriction and platelet aggregation were more pronounced and the vascular leakage was prolonged. This antigen dose also caused a massive PMNL accumulation in small venules, which coincided with the prolonged vascular leakage. Histamine was released in the reaction as pretreatment with mepyramine largely inhibited the leakage response to 1 microgram/ml OA. With 100 micrograms/ml OA, only the initial phase of vascular leakage was inhibited by mepyramine, leaving the prolonged vascular leakage and PMNL accumulation unaltered. Pretreatment with methylprednisolone 16-18 h prior to the experiments reduced both phases of vascular leakage as well as the PMNL accumulation. Pretreatment with the combined cyclo- and lipoxygenase inhibitors BW755C or nordihydroguaiaretic acid (NDGA) reduced the initial vasoconstriction induced with 100 micrograms/ml OA, thereby augmenting the initial vascular leakage. Despite this, the prolonged phase of vascular leakage was reduced in the NDGA-treated animals. Cyclooxygenase products were not found to play a crucial role in mediating the vascular response; on the contrary, indomethacin pretreatment slightly potentiated the vascular leakage induced by the low antigen dose.

An isolated perfused rat mesentery model for direct observation of the vasculature during cryopreservation

An intact vasculature is essential for successful hypothermic perfusion and cryopreservation of solid organs, but few studies have specifically assessed the vascular effects of these procedures. A technique was therefore developed for continuous, direct observation of an isolated vascular bed during hypothermic perfusion with cryoprotectants, and during freezing and thawing. The isolated rat mesentery was spread across a controlled low temperature microscope stage and perfused with solutions containing fluorescein isothiocyanate (FITC)-Dextran 70 as an indicator of macromolecular permeability of the vessels. Hypertonic citrate washout, HP-5 perfusion (23), rapid and slow addition and removal of glycerol, and freezing/thawing were studied. Control perfusion with HP-5 produced slow FITC-Dextran leakage, reflecting normal physiological macromolecular permeability of vessels. Rapid addition of glycerol dramatically increased vascular permeability, consistent with osmotic damage to vessels. Rapid removal stopped flow through capillaries and decreased vascular dimensions, suggesting overhydration of endothelial cells and extravascular tissue. Venules and capillaries were the most susceptible vessels to osmotic stress. Slow addition and removal of glycerol (80 mmol/liter/min) produced results similar to control perfusions. During slow freezing (0.5 degree C/min to -5 degrees C) extravascular ice compressing vessels was more obvious than intravascular ice. Glycerol afforded some protection to the microvasculature during freeze/thaw cycles since flow was reestablished in venules and arterioles after thawing, although FITC-Dextran leakage indicated that damage had occurred.

Effects of steroids and nonsteroid anti-inflammatory agents on vascular permeability in a rat glioma model

Cerebral edema produced by brain tumors is clinically and experimentally reduced by steroid therapy. Nonsteroid anti-inflammatory drugs (NSAID's) which have been used to treat non-neural inflammation and swelling have not been evaluated for their ability to affect edema produced by brain tumors. The authors have used the rat C6 glioma spheroid implantation model to compare the effects of two steroids (dexamethasone and methylprednisolone) and two NSAID's (ibuprofen and indomethacin) on protein extravasation caused by intracranial gliomas. Evans blue dye was used as a marker for serum albumin extravasation. The concentration of Evans blue dye was measured in the tumor and peritumoral and contralateral brain tissue 1 hour after intravenous injection. Extravasation of Evans blue dye within the tumor was decreased in all treatment groups when compared to placebo-injected control animals. The differences between the control specimens and those treated with dexamethasone, methylprednisolone, and indomethacin were highly significant (p less than 0.005). The Evans blue staining was also decreased in the peritumoral and contralateral brain. These results indicate that NSAID's compare favorably with steroids in diminishing tumor-induced protein extravasation. It is suggested that NSAID's may prove to be beneficial in clinical instances used either in conjunction with steroid therapy or alone when steroids are contraindicated.

Surgical exposure induces formation of an arteriovenous permeability gradient for macromolecules in the microcirculation of muscle

Rous and his colleagues (P. Rous, H. P. Gilding, and F. Smith, 1930, J. Exp. Med. 51, 807-830, F. Smith and P. Rous, 1931, J. Exp. Med. 53, 195-217) uncovered evidence for an arteriovenous gradient of permeability in exchange vessels of muscle. After injecting vital dyes intravenously in laboratory animals, including mice and rats, they examined escape of the dyes from exchange vessels of abdominal muscles, prepared for observation by reflection of the overlying skin. They noted that a particular class of dyes, termed "poorly diffusible," escapes from venules but not from arterioles and capillaries a few minutes after injection. We now assume that the "poor" diffusibility of the dyes stems from their binding to plasma proteins. We repeated similar experiments in mice and rats, using Evans blue as tracer, and also observed leakage of Evans blue from venules but not from other exchange vessels. We made three additional observations. (1) Evans blue leaks from venules only after the skin overlying the abdominal muscles is reflected. (2) Reflection of the skin initiates degranulation of mast cells in the muscles. (3) Leakage of Evans blue from venules is inhibited by administration of promethazine, a histamine and serotonin antagonist, to the animals prior to reflection of the skin. On the basis of our observations, we conclude that the arteriovenous permeability gradient for poorly diffusible dyes in the microcirculation of muscle represents response to tissue injury resulting from reflection of overlying skin.

Segmental differences of microvascular permeability for FITC-dextrans measured in the hamster cheek pouch

An intravital microscopic method for quantitative measurement of interstitial concentrations of fluorescent tracers has been applied to the investigation of microvascular permeability in the hamster cheek pouch. Some nanoliters of FITC-dextran mean mol wt (Mw) 20,000, 3000, or sodium fluorescein (Mw 376) were injected into an arteriole of the exposed cheek pouch via micropipet. The extravasation of fluorochromes was measured by a photodensitometric method including two sets of calibration procedures (in vitro and in vivo). Postcapillary and collecting venules exhibited the highest absolute increase of fluorochrome concentration in the tissue for all tracer molecules tested when compared to arterioles or capillaries. The permeability of the vascular wall was quantified, assuming that diffusion processes play the main role for the transport of the investigated molecules under the experimental conditions of a high concentration gradient across the membrane. Permeability coefficients P (cm/sec) and apparent diffusion coefficients D' (cm2/sec) of the microvascular wall were calculated using a mathematical model for one-dimensional diffusion in composite media. The analysis is based on measured data of interstitial diffusion coefficients of the tracers used. For all tracer molecules tested, the wall of the capillaries and postcapillary venules was significantly more permeable than the arteriolar wall. For the largest test molecule (FITC-dextran Mw 20,000), the permeability coefficient of the vessel wall showed a maximum in the postcapillary venules. These findings support the concept of a "gradient of permeability" with a nonuniform distribution of exchange capacity only for the precapillary microvessels. A marked preponderance of venular over capillary permeability could, if at all, only be detected for FITC-dextran Mw 20,000. The present study characterizes the vessel wall by apparent diffusion coefficients which are, for FITC-dextran Mw 3000, and free fluorescein, roughly three orders of magnitude lower than the apparent diffusion coefficients in connective tissue.

Indomethacin, (-)-terbutaline (beta 2 agonist), and (+)-terbutaline in acute inflammation induced by repeated ischemia in hamster cheek pouch

A mild and controlled acute inflammatory reaction in hamster cheek pouch was created without any exogenous, but rather by locally activated and liberated, mediators. A pressure of 60 mm Hg was applied to part of the everted cheek pouch eight times with a 10-min recovery period in between. The microvascular response was followed by intravital microscopy and the permeability changes were monitored with intravital fluoroscopy and intravenous FITC dextran (mol wt 150,000). The number of extravasated polymorphonuclear leukocytes (PMNLs) was calculated by a new, whole tissue, histological technique. In three experimental groups (-)-terbutaline (beta 2-receptor agonist) 0.05 mg/100 g body wt., (+)-terbutaline 0.05 mg/100 g body wt., and indomethacin 2 mg/100 g body wt. was given intravenously before pressure was applied. A fourth group, with no drug given, served as control. There was a rapid increase in the number of FITC dextran leakages and extravasated PMNLs in the control group. Indomethacin almost completely inhibited FITC dextran permeability and extravasation of PMNLs. The beta 2 agonist markedly diminished the number of FITC dextran leakages for 75 min. The number of extravasated PMNLs was also reduced. Treatment with (+)-terbutaline, which is supposed to have no beta 2-receptor effect, gave a slight reduction in number of FITC dextran leakages and almost a complete inhibition of PMNL extravasation. Thus we conclude that indomethacin is a very potent antiinflammatory agent even in the early phase of inflammation. (-)-Terbutaline diminished the inflammatory response, probably by preventing endothelial gap formation. (+)-Terbutaline prevented PMNL extravasation either by interaction with the PMNL itself or with the endothelium.